Non-Capturing Group(?:https?:\/\/)? ?repeats the group contents below at most once:
httpthe literal text http (case insensitive) s?optionally matches the literal s (11510 / 1638 / 7316) (case insensitive)
:the literal : (5810 / 728 / 3A16)
\/the literal / (4710 / 578 / 2F16)
\/the literal / (4710 / 578 / 2F16)
wwwthe literal text www (case insensitive) \.the literal . (4610 / 568 / 2E16)
youtubethe literal text youtube (case insensitive) \.the literal . (4610 / 568 / 2E16)
comthe literal text com (case insensitive) \S+?any non-whitespace character, repeated at least once
v=the literal text v= (case insensitive) \Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
\S+any non-whitespace character, repeated at least once
g modifier: global. Finds all matches instead of stopping after the first
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters